1. Field of the Invention
The present invention relates to a process for continuously guiding liquids when digesting pulp in a digester.
2. Discussion of the Background
In a modern pulp digestion process, several steps are required, thus, among others, an impregnation under particular process conditions, e.g. at a low temperature, and digestion under different conditions, e.g. at a higher temperature, as well as, if desired, one or several washing steps, which are effected by using hot and/or cold washing liquid or washing filtrate, respectively. For the production of pulp, the solvents used in the individual process steps for the dissolving out of certain components must have certain properties, such as, e.g., the type of solvent, whether aqueous or organic, concentrations of acids, alkali and salts, temperatures, etc.
For reasons of costs and last but not least for environmental reasons it is desirable to keep the amount of chemicals and the liquid required in the individual steps as low as possible and to re-use the solvents utilized to the greatest possible extent.
According to WO 91/05103, preconditioned wood chips are preheated in a first chamber by means of circulating black liquor at a low temperature and are continuously fed into a second chamber at high pressure and temperature. In the second chamber, the wood chips are advanced to a cooking temperature by circulating hot black liquor, whereupon they are transferred into the digester together with white liquor.
U.S. Pat. No. 4,693,785 relates to a digester for continuous processing. Supply and discharge of the liquors used are effected via a plurality of annular screen systems.
In U.S. Pat. No. 3,752,319, a strainer for separating liquid from a wood chips-liquid-mixture is described.